For children, - Takabbur in Islam: Pride in Islam, Arrogance - Kibr is a barrier to Paradise

A proud and arrogant person regards himself better and superior to
others and by assuming vain and wishful thoughts in his mind, adopts
the conduct of Shaitan (Satan) who said: "I have been created of fire
while Adam has been created of earth and fire possesses superiority
over earth." The first sin to have been committed in the world of
creation was arrogance on the part of Shaitan (Satan).
This pride and prejudice on the part of Satan is what caused his
downfall - and has the potential to affect each and every one of us.
Satan felt that his physical makeup of 'smoke-less fire' was of a
loftier composition, and that being made of fire, he had the potential
and was naturally inclined to 'ascend' (just as fire does), whereas
the makeup of Adam was of 'earth', a heavier compound, and that his
natural inclination was to the base, lower desires, and to clinging to
the 'earth'.
Thus, as for it being a vice, there can be no doubt or skepticism.
Proud and arrogant individuals look down upon others and anticipate
others to greet them and exhibit respect and deference towards them,
always nurturing aspects of their superiority and greatness within
their minds. This "puffed up" feeling which imparts a sense of "touch
me not" is called pride (Kibr/Takabbur).
The condition of conceit and of one who considers himself to be
greater than others, so long as it stays inwardly and has no outward
manifestation, it is pride. If it gets out through the senses, it is
called arrogance.
Arrogance is one of the consequences of vanity and self-conceit. When
an individual thinks too highly of himself, it is self-conceit; and
when he tends, moreover, to consider others as inferior to himself,
that is arrogance. In contrast to these states, when one thinks of
himself as small and insignificant, that is called modesty; and when,
in addition to this, he considers others as superior to himself, that
is called humility. In any case, arrogance is one of the most fatal of
moral vices. This is so because arrogance is a thick veil which hides
one's shortcomings from his own view, and thus prevents him from
removing them and attaining perfection.
Arrogance is a mental state causing self-admiration and haughtiness
against others in words or deeds. It is censured and dispraised in
many texts in Noble Qur'anand Sunnah:
Truly Allah knows what they hide and what they manifest; surely He
does not love the proud. Noble Qur'an (16:23)
Holy Prophet of Islam, Muhammad (saw) says: "He who has in his heart
as much faith as a grain of mustard seed will not enter hell, and he
who has in his heart as much pride as a grain of mustard seed will not
enter paradise." Hence, Pride (Kibr/Takabbur) is a barrier to
Paradise.
A proud man will not tolerate any other to be on equal terms with
himself. In private and in public he expects that all should assume a
respectful attitude towards him and, acknowledging his superiority,
treat him as a higher being. They should greet him first; make way for
him wherever he walks; when he speaks everyone should listen to him
and never try to oppose him. He is a genius and people are like asses.
They should be grateful to him, seeing that he is so condescending.
Virtues are the doors of Paradise, but pride and self-esteem lock them
all. So long as man feels elated he will not like for others what he
likes for himself. His self-esteem will deprive him of humility, which
is the essence of righteousness. He will neither be able to discard
enmity and envy, resentment and wrath, slander and scorn, nor will he
be able to cultivate truth and sincerity, and calmly listen to any
advice. In short, there is no evil which a proud man will not
inevitably do in order to preserve his elation and self-esteem.
Being proud about ones own piety is a major sin. This pride can make
all the prayers and supplications void. If a person understands the
Greatness of Allah (SWT), then he will not be proud and vain at his
exertions at prayer. The endowments of the munificent Allah (SWT) are
so great that it is impossible to count His Blessings.
Imam Jafar al-Sadiq (as)who cites Holy Prophet of Islam, Muhammad
(saw) in a tradition in which Hazrat Musa (Moses) son of Imranasks
Satan. "Tell me about the sin which, when a son of Adam commits, you
overtake him." Satan replied, "It is when he is proud of himself,
thinks too much of his good deeds and his sin looks small in his
eyes." It is known that when Satan overtakes someone, the result will
be more sinning.
Imam Ali Reza (as)says that a pious person from Bani Israel offered
intense prayers for forty years. Then he offered a sacrifice to Allah
(SWT) that was not accepted. The person was disconsolate with sadness
for his failure. He cursed his psyche blaming it for his failure. He
received a Revelation that blaming his psyche and accepting the
shortcomings pleased Allah (SWT) more than the prayers spread over the
long period of forty years. For this reason Allah (SWT) accepted his
long years of penance.
Imam Mohammed Baqir (as)says that two persons entered the mosque. One
was pious and the other a transgressor. When they emerged from the
mosque after the prayer, the transgressor was pious and the person
with piety had turned a transgressor. The reason was that the pious
person came out of the mosque with pride at his piety and the
transgressor was penitent at his past misdeeds.
Imam Ali (as)says: "The sin that makes you sad and repentant is more
liked by Allah (SWT) than the good deed which turns you arrogant."